Filling gas bottles.

[Bobobolinsky]

Since you have a saturated gas/liquid mix in the tank, pressure is dependent on temperature and nothing else. As long as there is a some gas there when you fill, and you don't pump it, I can't see how overpressuring could arise. When I fill my car with LPG it is pumped, so the fuel in the tank warms slightly and the consequent pressure increase shuts off the pump at about 85% full: less if filling from near empty, more if it was almost full when I started.



Good idea, but as long as you don't let it squirt on flesh - or smoke - a tube full of liquid propane isn't a particular problem.

Nope, the tank in your vehicle has a level guage, which cuts off the flow at 85%
Overfilling a cylinder, will hydraulically pressure the tank. This is unlikely to rupture the tank as the pressure relief valve will lift, but the noise as it lifts is a little scary and don't have any naked flames around when it does.

 

[vyv_cox]

I believe that the rubber high pressure hoses are not designed to carry gas in liquid form. They have no problem with the pressure, but I've read somewhere that the liquid will degrade the materials over time. I use one, but I'm keeping a very good eye on it.

It's a very long term problem. In caravans and motorhomes exposure of rubber hoses to liquid propane or butane over years causes some plasticiser to leach out and re-deposit itself in the bulkhead regulator. In a few cases this has led to liquid or high pressure gas reaching the cooker, with exciting results. Could be more of a problem in boats due to heeling introducing liquids to the hose, but on the other hand bulkhead regulators seem to be far less common on yachts.

I have all-stainless HP hoses in my motorhome for this reason.

 

[prv]

Could be more of a problem in boats due to heeling introducing liquids to the hose

The activity being proposed here seems to be to "pour" the liquid from one cylinder to the other, by placing the donor one higher and upside-down. So it would definitely involve applying plenty of liquid "gas" to the hose, not just the odd bit of splashing while heeled.

Bear in mind that gas bottles are routinely filled from others in various situations. Dive clubs decant from high pressure storage tanks into dive cylinders and the pressures here are around 200bar. [...] My tig gas supplier does the same with argon at 230bar.

But both of those are exclusively gasses. If this was the same I'd have been a lot quicker to call "bull****" on the naysayers, since I understand transferring gas (in a diving context) reasonably well. The difference here is that most of the "gas" is actually liquid, and you have the equilibrium between the two phases. That's outside my experience, so I'm a lot more circumspect about the possible problems. The talk of over-pressurising the cylinder by not allowing enough head-space for instance - sounds at least vaguely plausible, and I don't feel qualified to judge either way.

Taken to its conclusion, is there a possibility of incorporating gas storage as a permanent tank just as with propulsion fuel?

I believe it is, or was, done in the US. I vaguely remember a bit in one of the Pardey books where they mentioned the custom steel tank they had fitted in their first boat, which left rust stains, and how they tried to get a custom aluminium (non-rusty) tank for their second but were told that the different manufacturing process made it uneconomic to do one-offs. They instead designed a box to take three standard cylinders, but the implication was still that they had them refilled rather than exchanged.

Pete

 

[vyv_cox]

The activity being proposed here seems to be to "pour" the liquid from one cylinder to the other, by placing the donor one higher and upside-down. So it would definitely involve applying plenty of liquid "gas" to the hose, not just the odd bit of splashing while heeled.

Yes, but not through a regulator. Decanting through rubber hoses is a long way from the problem the previous poster was concerned about. Just attempting to clarify.

 

[Ubergeekian]

Nope, the tank in your vehicle has a level guage, which cuts off the flow at 85%

Does it? Coo, I didn't know that. Thanks. Different pumps on different days can get different amounts in - the variation is about 15L.

Overfilling a cylinder, will hydraulically pressure the tank. This is unlikely to rupture the tank as the pressure relief valve will lift, but the noise as it lifts is a little scary and don't have any naked flames around when it does.

True, but you won't over pressurise by connecting two tanks together. It's a lot simpler with no pump.

 

[saltylegs]

Yes, I've seen the after effects of a gas explosion at close quarters. It was in entirely different circumstances and those that caused it were lucky to escape. However, let me press you on what you saw...........not the gory details but the actual cause of the problem.

Ok
lets forget the stupid stuff like smokeing etc.
when decanting from domestic type transportable cylinders you will find that due to the cylinders being banged around a lot there is usually slag in the bottom of the cylinder as well as a build up of heavy ends ( an oily residue of compounds that do not vapourize into the gas), during the decanting process these items can lodge on the seat of the valve of either cylinder and cause a leak, and due to the transfer process causing a drop in pressure in the delivery vessel this leak is not easy to spot until the remaining liquid can fully vapourize and thus repressurize the cylinder so now you have a leaking cylinder, although it is more common for the valve on the recieving cylinder to fail.

other problems that can crop up is freezing of the delivery hose (mainly with propane) and in extreme cases and with substandard hoses this can lead to the hose failing as it can become so brittle that it is easliy broken.
When inverting the delivery cylinder this can also cause the connections to loosen causing a leak which you dont notice as you are expecting to smell gas anyway and burns are very common when dissconecting the transfer hose due to the trapped liquid.
persons then putting that hose away with the liquid trapped in it and there is no pressure relief valve fitted so as it heats up the pressure increases and goes pop.

some posters seem to think that because there is a PRV fitted to most cylinders (not always on some of the smaller ones) that they dont have to worry about over filled cylinders but alot of these fail to reseat when they blow leaving an uncontrolled leak.

the above are actual causes of "incidents" that I have come across,

I will post below here on some of the other points raised

 

[nimbusgb]

I have just spent 2 days at the Caravan and camping show at the NEC. There's a stand there with equipment for refilling your own cylinders. There was a lot of interest on the stand.

Sorry it did not mean anything to me at the time, I was working on other things but it would appear to be above board.

Perhaps a troll of the NEC show website might turn up the name of the company.

I used to fill my own O2 bottles when flying in the mountains. A bit of care and the right equipment and there's nothing to be worried about, those cylinders were at 3000 psi iirc.

 

[saltylegs]

weighing cylinders
the main cylinder gas suppliers fill the cylinders on automated and calibrated scales the operatives visually inspect the condition of the cylinder and seal before it enters the conveyor system the tare weight of the vessel is then entered and and when the correct weight of product is achieved refilling stops, the valve is then checked with LDF (soapy water) and seal or plug/cap fitted.

Cylinders are only pressure tested and revalved if they have reached thier test date or are showing signs of damage.

Automotive type vessels on boats, these are fitted already to LPG powered craft and are of the liquid draw of type, the shape of this type of vessel means it is not practicale for vapour offtake on a boat due to the risk of liquid entering the supply hose.

It is common for automotive vessels to over fill normally indicated by getting about 15% more in than you normally do and this is due to a faulty automatic max fill valve, this does not normally cause a problem as the car is driven off thus lowering the amount of liquid in the vessel.

there are some refillable cylinder systems available from uk suppliers put they tend to be too large for most of our applications, and the last time I priced them i reckoned pay back would be over 15 years.

if something else comes to mind iwill edit it in.

 

[saltylegs]

I have just spent 2 days at the Caravan and camping show at the NEC. There's a stand there with equipment for refilling your own cylinders. There was a lot of interest on the stand.

Sorry it did not mean anything to me at the time, I was working on other things but it would appear to be above board.

Perhaps a troll of the NEC show website might turn up the name of the company.

I used to fill my own O2 bottles when flying in the mountains. A bit of care and the right equipment and there's nothing to be worried about, those cylinders were at 3000 psi iirc.

most common one in the UK is a company called Gas Lo

 

[dratsea]

You have my full support (been doing it since 1998!). For the feint hearted please be assured that it is amazingly difficult, I believe impossible, to overfill an (empty) American 20lb cylinder from a 6Kg calor cylinder, but for those of less pecunious means, who happen to possess a pair of digital luggage scales, it is cheaper to use the 19Kg.

PS, safe on board, but probably not down below!

 

[Rigger Mortice]

A few thoughts on some of the comments which have been made. Forgive me for not quoting everyone....I don't want this to run over several screens.

1. Overfilling. Nigel Calder talks about not filling bottles to more than 80% of their capacity (and adds that in hot climates you should work to 70%). In many ways this is academic as the calculation has already been done. The tare weight of the cylinder is already stamped on it. The maximum fill, as far as I am concerned, is the declared weight; it would be daft to go any higher. Final filled weight is therefore tare weight plus declared weight. This is what the suppliers work to so, if it's good enough for them......
Being cautious, I have slightly underfilled.

2. Is weighing the best method to use? Well, the suppliers use it!
More importantly, I doubt that pressure testing or filling by volume would be accurate as I assume both methods would be subject to variation due to temperature.

3 Pressure testing at the manufacturers. Yes, I have thought about this. I'm inclined to think that the best thing would be to buy refilled cylinders every now and again.....maybe every three years, but I'm not sure.
I don't think for one minute that the manufacturers would be happy about this but they don't seem to be concerned about the fact that I don't like their pricing policies.

4. Scales. I certainly would not use bathroom scales without very carefully checking them beforehand. They are notoriously inaccurate (ask any woman!). I have been using some old kitchen scales which I know to be accurate as I have access to accurate scales at work.
Other than that, as a stand by; 1 litre of water =1kg!

5. Warming the bottles. Again, Nigel Calder mentions this and takes it one stage further. He recommends putting towels on both cylinders and then pouring hot water on the donor bottle and cold water on the recipient bottle. It seems sensible.

6. Emptying the hose when finished. It seems sensible to not leave it under pressure and even more sensible to take care not to get freezer burn on your fingers when clearing the hose!

7. Valve leaks. I don't like the idea of bunging a screwdriver down on the valve to help reseat it; it would be too easy for the screwdriver to slip and damage the seal or the valve.
I did have one occasion when the valve had not reseated properly......there was a barely audible hiss of escaping gas. (FWIW I've also had this problem when removing the regulator when on the boat, so it's not just down to being a problem when refilling.)
My solution was to put the adapter (or regulator when on the boat) back on the bottle turn on, turn off and remove again. This opens and closes the valve in the way it was intended to be used.

8. Soapy water. Yes, we all know we should do this, but always put it off. Promise to self; USE SOAPY WATER, IT'S EASY TO DO!

9. Liquid gas on the hoses. I really can't comment other than to take note of what has been said above.

10 Muck in the bootles. I wasn't aware of this. If the problem is just with the valves not seating properly then a combination of soapy water and 7 above will , I hope, resolve it....but it needs more thought!

11. Freezing and substandard hoses. I'm only interested in doing this with butane which helps but, so far, I've had no problems with freezing though things have obviously got a little colder. I am wondering if this will become more of a problem when the weather warms up?
I've used BS hoses which is as far as I can go as I certainly don't have any testing facilities (or knowledge!). I am however a bit more concerned about mechanical damage resulting in problems. It may be sensible to replace the hoses after a sensible period.

12. I'm a little surprised that freezer burns are common as I had assumed that this was an obvious problem....however, comments duely noted and will be born in mind. (that is meant seriously, not sarcastically!)

13. I didn't know that Camping Gaz cylinders were purchased outright. That puts my mind at rest as it means that it's nothing to do with them!

14. I did read the Calor Gas agreement sometime ago. The bottle remain theirs and even if we buy them from elsewhere that doesn't mean that we "own" them. They still remain Calors property and, in theory, they could recover them. All very academic and I rather doubt that Calor would do anything about it if you phoned them and said "some of your bottles have been dumped in the local canal, will you remove them?"

Thanks for all the input and, in particular that of SaltyLegs...it's useful to have the benefit of experience. As well as trying to reduce costs this is also about trying to reduce risk to me and mine and those around me!

 

[saltylegs]

Cheers Rigger Mortice

as a PS to your last line if you reported dumped / abandoned cylinders to the main cylinder suppliers then they will have them collected.
the fire service report them all the time in relation to bonfires etc.

 

[VicS]

This is something that you obviously can do and with care and a decently constructed set up you can do safely.

My comments

By weight is the only practical method of measuring the quantity of gas transferred. Pressure as, has already been said, is dependent on the temperature and not on the quantity of liquid in the bottle.
I cannot think of a practical method of measuring the volume transferred. You have no data to relate to anyway.

Because the pressure is solely dependent on tempearture, transfering between two bottles at the same temperature will be painfully slow. That is why Calder suggests warming the donor bottle and cooling the recipient bottle.
As warm liquid flows into the recipient bottle it will slowly warm so continuous cooling will help.

Regarding pressure testing. There will be no problems swapping cylinders at intervals of several years if that is what you feel should be done. Some of my Gaz bottles have not been refilled for very many years. The filling depot will not know what I have been doing with them ( In fact nothing. There are four out in the garage varying between MT and half full.)

Filling dive bottles etc is a different ball game. The gases do not liquefy when pressurised. They will only liquefy if cooled below the "critical temperature" That's -118C for oxygen , and -147 C for nitrogen. The quantity of gas in the bottle can be measured by pressure and mixtures made by pressure measurement.
There is no need to invert the donor bottle or to use any warming or cooling.


BUT BUT BUT

If you have mishap that results in injury or damage to a third party's property the courts will have field day with you!

Just which of your insurance policies will pay out in the event of claim against you.
Let me guess. Not one of them. You'll be selling your boat, your car and your home to pay the damages yourself ...

 

[Graham_Wright]

Interesting thread. What medium do they use for pressure testing. Same gas?

Should be a liquid to avoid explosions.

 

[Rigger Mortice]

[COLOUR="Red"]BUT BUT BUT[/COLOUR]
If you have mishap that results in injury or damage to a third party's property the courts will have field day with you!

[COLOUR="Red"]Just which of your insurance policies[/COLOUR] will pay out in the event of claim against you.
Let me guess. Not one of them. You'll be selling your boat, your car and your home to pay the damages yourself ...

Vic,
Thanks for your comments on the technical issues.
However, despite your vivid portrayal of the doomsday scenario, I will refrain from saying "Yes, but"...it will only result in yet another debate about legal issues which none of us are really qualified to talk about. There's more than enough barrack room lawyers on this site and I do not wish to become yet another.

What I would say is that, for me, this little "project" has been about trying to find how to fill bottles safely and that, of course, means trying to recognise and manage the risks which are involved. Obviously there is a risk of it all going "boom" and that needs to be taken seriously, but it is interesting that none of the incidents which Salty Legs described appear to involve an explosion. It looks as if they were more "near misses" than anything else. (I'm sure that he will let us know if that is wrong).

I have no desire to trivialise the potential problems but, by neither do I wish to make a melodrama of the possible outcome. I've already learnt a lot from the input of others, including yourself!

On another but related subject: Last night, I checked the price of butane cannisters (250gm "aerosol" cans). They are readily available at prices far lower than Camping Gaz meaning that it is considerably cheaper to cook using one of those cheap camping cookers than it is to use rip-off Camping Gaz.

 

[VicS]

On another but related subject: Last night, I checked the price of butane cannisters (250gm "aerosol" cans). They are readily available at prices far lower than Camping Gaz meaning that it is considerably cheaper to cook using one of those cheap camping cookers than it is to use rip-off Camping Gaz.

Keeping my doom and gloom hat on for a moment there was problem a while back with some of the little stoves that run on those cannisters.

I am sure it has long been sorted. It revolved around the fact that they could be assembled incorrectly IIRC

Made known by the BSS people. The link is http://www.boatsafetyscheme.com/dow...sstovessafetyalertBSSWebversionAPR09FINAL.pdf

 

[saltylegs]

Hi
As you said you did not want the gory details I did not (and could not) give them however I will say that none of the examples that I refered to were fatal.
However all resulted in expolsion, fire or both and most involved injuries.
When people have near misses they tend not to put their hands up and say opps I may have been a bit silly, so it is usually when it is reported by a third party, either the services or when someone hears the bang or sees the smoke.

 

[Rigger Mortice]

Well that's ruined that point for me!
...and you are right not to go into unnecessary detail. It's the internet equivalent of rubber necking.

 

[Conachair]

Thanks for the thread!
Gee-ed me up to finally getting round to ordering some adaptors to fill the Usa propane bottles I have from callor bottles. No prob overfilling as they are grp and you can see the level of the gas.

The post about butane only in butane bottles is a bit confusing though - is that right? For sure don't put propane in butane bottles, but the other way round? Last time I got these bottles filled it was a mix butane/propane.

 

[sarabande]

The GasLow site recommended by Saltylegs seems to know a lot about supplying the necessary parts.

http://www.motorcaravanning.co.uk/pdf/Gaslow-Aug-2009-brochure.pdf


An impressive brochure, BTW!